1. Field of the Invention
The present invention relates in general to an optical pick-up device of optical disc players such as a laser disc player (LDP), a compact video disc player (CVDP), a compact disc player (CDP) and etc., and more particularly to an optical pick-up device which does not require a servo mechanism for carrying out the mechanical movement of an optical pick-up head but comprises an acoustooptic deflector for scanning the laser beam to the optical disc simultaneously with deflecting the laser beam to a desired direction.
2. Description of the Prior Art
With reference to FIGS. 1 and 2 showing a known optical pick-up device of an optical disc player, the known device generally comprises an optical pick-up head part 10 for recording/playing back the data on/from an optical disc 1. This known device is also provided with a servo mechanism for controlling the precise movement of the optical pick-up head part 10 with respect to the optical disc and the data recording/playing back operation of the part 10.
As shown in FIG. 2, the optical pick-up head part 10 comprises a laser source, that is, a laser diode 11 for generating a laser beam, a collimator 12 for collimating the laser beam from the laser diode 11 so as to make this beam become a parallel beam. Under the collimator 12, a beam separator 13 and an objective lens 14 are sequentially arranged as spaced apart from the separator 13 and also from each other. Here, the beam separator 13 receives two types of incident laser beams, the one being received from the collimator 12 and the other being reflected by the optical disc 1, and causes the one laser beam to be scanned to the optical disc 1 while it reflects the other laser beam in order to separate the laser beam. On the other hand, the objective lens 14 receives the laser beam from the beam separator 13 and focuses this laser beam on the optical disc 1. When the laser beam is focused on the optical disc 1 by the objective lens 14, this laser beam has the shape of a minute beam spot. If the laser beam reaches a desired position of the optical disc 1, it is reflected by the disc 1. At this time, the objective lens 14 receives such a laser beam reflected by the disc 1 so as to make this beam become a parallel beam which is in turn received by the beam separator 13. In addition, the pick-up head part 10 includes a condenser lens 15 for condensing the laser beam which has been reflected and separated by the separator 13. An optical detector 16 is provided so as to detect the condensed beam from the condenser lens 15 in order to output an electric signal corresponding to the detected laser beam.
On the other hand, the servo mechanism of the known device comprises a guide rail 21 for guiding the movement of the pick-head part 10 so as to cause this part 10 to be located at a desired position above the optical disc 1. At an end of the guide rail 21, a step motor 22 for controlling the movement of the pick-up head part 10 along the rail 21 is disposed. In addition, this servo mechanism is provided with a servo circuit 23 for controlling the operations of both the step motor 22 and the pick-up head part 10.
In operation of the above optical pick-up device, the laser diode 11 of the optical pick-up head part 10 generates a laser beam which is in turn received by the collimator 12 in order to be collimated thereby. This collimated laser beam is then received by the beam separator 13 and in turn focused on the optical disc 1 by means of the objective lens 14. When the laser beam is focused on the disc 1, this beam becomes a minute beam spot by addition of the objective lens 14.
Upon being focused on the disc 1, the laser beam is reflected by the disc 1 and received by the beam separator 13 by way of the objective lens 14. By this beam separator 13, the received laser beam is reflected in order to be condensed by the condenser lens 15. This condensed beam is then received by the optical detector 16 which detects the laser beam and outputs electric signals proportional to the intensity of the laser beam reflected by the disc 1, thereby causing the data recorded on the disc 1 to be detected.
On the other hand, in order to permit the optical pick-up head part 10 to record and to play back the data on and from the optical disc 1 using the laser beam, it is required to precisely control the movement of the optical pick-up head part 10 by means of the servo mechanism.
In other words, the servo circuit 23 controls the step motor 22 in order to drive the optical pick-up head part 10 to move to a desired position above the optical disc 1 as guided by the guide rail 21. Here, each track of the disc 1 conventionally has a minute width of a few micrometers. Hence, in order to accurately locate the optical pick-up head part 10 above a predetermined track of the disc 1 which is intended to be accessed by the head part 10, the movement operation of optical pick-up head part 10 is necessarily precisely controlled in consideration of mechanical inertia caused by the movement of the head part 10 and the like.
The known optical pick-up device of the optical disc player thus requires to be equipped with a precise servo mechanism which can make possible to precisely control the movement of the optical pick-up head part 10 within a minute range of a few micrometers. Furthermore, this known optical pick-up device requires a high level of circuit technique for improving the accuracy of its operation. In addition, there is the inevitable limitation in reducing the access time due to the mechanical movement of the optical pick-up head part 10.
Also, in order to accomplish the precise location of the pick-up head part 10 with respect to the optical disc 1, the servo mechanism must be precisely operated so that it inevitably has a disadvantage in that it has no resistance to a mechanical shock such as an outer vibration. Particularly, in such a servo mechanism, the guide rail 21 must be machined so as to have a high machining accuracy and this causes the manufacturing cost to be unwillingly increased.